Ships and boats at sea need a variety of information in order to navigate safely. This information includes: the vessel's position relative to its planned course; the vessel's position relative to visible navigation hazards such as land masses and other ships; and the vessel's position relative to hidden hazards such as submerged rocks, channel boundaries, shipping lane separation zones, and restricted areas. The mariner acquires this information in a number of ways.
The first is by visual reference. By monitoring the vessel's position relative to known points of land, often with the aid of a compass, the navigator can triangulate the ship's position relative to its intended course. By monitoring other vessels, the navigator calculates whether a course change will be required to avoid a collision. And, by monitoring the ship's position relative to buoys, lights, and other visual aids to navigation, the mariner can also avoid some of the unseen hazards to navigation.
This same information is commonly augmented by radar which also displays the ship's position relative to visible hazards such as land masses and other vessels. In addition, the radar, with input from the ship's gyro or magnetic compass, can more accurately calculate range and bearing and perform collision avoidance calculations.
To best avoid unseen navigation hazards such as submerged rocks, the navigator needs to continuously calculate the absolute geographic position of the vessel and plot that position against a nautical chart on which the hidden hazards to navigation are indicated. This process is greatly facilitated by use of a Global Positioning Systems (GPS) receiver and an Electronic Chart System (ECS). The ECS displays a digital representation of a conventional paper nautical chart. On this chart, the ECS overlays the position of the ship based on input from the GPS. The ECS usually consists of a navigation computer containing an electronic nautical chart (ENC) database, interfaces to navigation sensors such as those identified below, and a fairly high resolution computer display screen.
While the ECS represents a vast improvement over manually plotting the ship's position against a paper chart, it has a number of drawbacks and limitations. The first is that it is often difficult to relate: (a) the information in the electronic chart display (usually oriented course-up) with (b) the real world as seen from the navigator's field of view (often a completely different direction). A second significant limitation is that the ECS requires a color, fairly high resolution (therefore fairly large size) display to be most effective. Many mariners, however, navigate from an open cockpit or a flying bridge conning station. There, the lack of space, glare from direct sunlight, and exposure to the elements limit the utility of an ECS display.
Others have attempted to improve marine navigation by augmenting marine binoculars with information pertinent to navigation. Heretofore, these attempts have been limited to adding only bearing and, in a few cases, distance information. This information is at best of limited utility in identifying hidden obstacles and other unseen hazards to navigation. Furthermore, these products usually split the field of view between the real world image and an image of a compass, using mirrors and normal lens optics. This is awkward and can actually distract from instead of enhance the real world image available to the mariner.
From the foregoing, it will be apparent to the reader that there is a present and continuing need for better aids to marine navigation.